chore: skip lint on node v4

The lint command appears to be broken on node v4. It should be fine to
skip this on v4 though since we can run lint on >= v6.

Fixes #25

.github/workflows/main.yml

@@ -28,4 +28,7 @@ jobs:
         with:
           node-version: ${{ matrix.node-version }}
       - run: npm install
-      - run: npm run test
+      - run: npm run test-without-lint
+      - name: run lint (node >= 6)
+        run: npm run lint
+        if: matrix.node-version >= 6

package.json

@@ -6,6 +6,7 @@
   "scripts": {
     "posttest": "npm run lint",
     "test": "mocha",
+    "test-without-lint": "mocha",
     "lint": "eslint .",
     "changelog": "shelljs-changelog",
     "release:major": "shelljs-release major",